1. Field of the Invention
The present invention relates to a flat Braun tube, and more particularly, to a flat-tension shadow mask in a flat cathode ray tube.
2. Background of the Related Art
In general, the Braun tube(or a cathode ray tube) is employed in a TV or a display, and particularly, the flat Braun tube is used widely presently as the reduction of image distortion in the flat Braun tube improves a sense of vision, and the reduction of random reflection in the flat Braun tube reduces eye fatigue. A system and function of the related art flat Braun tube will be explained with reference to FIG. 1.
Referring to FIG. 1, the related art flat Braun tube is provided with a flat panel 1 having fluorescent material 3 coated on an inside, and a funnel 5 of a bulb form welded to a rear surface of the panel with Frit glass, to form an inner space at a high vacuum of 10xe2x88x927 Torr. There is a rectangular rail 7 in the inner space of the panel 1 and the funnel 5 fitted on an inside surface of the panel 1, to which a shadow mask 9 having fine perforation of slits or holes 11 for passing electron beams is fitted with a tension given thereto in advance. And, there is an electron gun 13 built in a bottle neck formed neck part 6 in rear of the funnel 5 for emission of electron beams(thermal electrons) as red, green, and blue three color picture signals are provided thereto, and a deflection yoke 15 outside of the neck part 6 for forming electro-magnetic fields in vertical and horizontal directions for deflection of the electron beams.
When a picture signal is provided to the cathodes(not shown) in the electron gun 13 of flat Braun tube, electron beams of red, green, and blue three colors are emitted toward the fluorescent material 3 coated on an effective area inside of the panel 1. Most of the electron beams(approx. 85%) is blocked by bridges 14 of the shadow mask( or flat-tension mask) 9 as the electron beams pass through the shadow mask 9 on an electron beam path, while rest of the electron beams(approx. 15%) pass through the fine holes 11 in the shadow mask 9 and collide onto red, green, and blue fluorescent materials 3 to reproduce a color picture.
In the meantime, if an impact or interferential acoustic wave is provided to the Braun tube from outside, the shadow mask 9 will vibrates. In this instance, as shown in FIGS. 2 and 3, since a position of the fine hole 11 (hereafter called as xe2x80x9cbeam pass through holexe2x80x9d) in the shadow mask 9 is varied with a vibration frequency, the electron beams can not pass through the beam pass through hole 11 regularly, but blocked by no-hole regions 12 and the bridges 14 periodically, to cause so called howling in which the picture shakes. In order to suppress this, a damping wire, a vibration attenuating means, is closely fitted to one side of the shadow mask 9. In this instance, the damping wire 8 is fitted across the no-hole region 12 between adjacent horizontal lines 11a and 11b of beam pass through holes in the shadow mask 9, by welding both ends to brackets 17 on the rail 7 under tension. And, there are reference holes 16 on both ends of a damping wire fitting path in the no-hole region 12 as reference points for aligning the damping wire 8 on an exact position of the no-hole region 12 by making the damping wire 8 to pass through the reference holes 16. However, keeping pace with the recent trend of requiring high definition TVs, an area for the damping wire 8 has been restricted as a pitch xe2x80x98Pxe2x80x99 of the beam pass through holes 11 becomes gradually smaller, causing the damping wire 8 to move into an area of the beam pass through hole 11 even by a minute vibration of the shadow mask 9, to display a shadow on a screen. And, there has been difficulty in fabrication in that burr formed in welding the rail 7 to the shadow mask 9 impedes fastening the damping wire 8 at an exact position by welding through the burr.
There is another method for fastening a plurality of damping wires 8(3 in general) each with approx. 60 xcexcm diameter under tension on the shadow mask 9 for controlling vibration of the shadow mask. In this instance, as the damping wire 8 has a diameter which is too small to weld itself on a rail assembly 7 directly, the welding is conducted under a condition a bracket 17 and a plate 21, both of which secure a welding area, are fitted on top and bottom of both ends of the damping wire 8. In a state each of the brackets 17 of a damping assembly formed thus is placed on a recessed step surface 7a of the rail assembly 7, the damping assembly is fixed to a top surface of the rail assembly 7.
However, in the related art damping wire, since the damping assembly has the bracket 17, the plate 21, and the damping wire 8 integrated as one unit, the damping assembly delays a Braun tube fabrication process and deteriorates an efficiency of the fabrication process as the damping assembly requires respective component fabrication processes, and a component integration process. Since the damping assembly is not closely fastened to the shadow mask effectively, the plurality of damping wires, in general 3, required for obtaining a damping effect of a desired level increases a number of components, that pushes up a production cost. And, the damping wire 8 coming into the area of the beam pass through hole 11 of the shadow mask 9 caused by shaky damping assembly deteriorates a picture quality. Since debris, produced when unnecessary edges of the shadow mask is cut off after the shadow mask is welded to the rail assembly and remained on a fastening surface of the damping wire 8, impedes close fastening of the damping wire 8 to the shadow mask 9, the related art damping wire can not provide a desired vibration attenuation effect required for the shadow mask.
Accordingly, the present invention is directed to a shadow mask in a flat cathode ray tube that substantially obviates one or more of the problems due to limitations and disadvantages of the related art.
An object of the present invention is to provide a shadow mask in a flat cathode ray tube, in which a damping wire can be fastened.at a more exact position and a fastening force between shadow mask and the damping wire are strengthened.
Additional features and advantages of the invention will be set forth in the description which follows, and in part will be apparent from the description, or may be learned by practice of the invention. The objectives and other advantages of the invention will be realized and attained by the structure particularly pointed out in the written description and claims hereof as well as the appended drawings.
To achieve these and other advantages and in accordance with the purpose of the present invention, as embodied and broadly described, the shadow mask in a flat cathode ray tube having a damping wire located across a no-hole region between adjacent lines of beam pass through holes formed on a vertical line in the shadow mask for damping vibration of the shadow mask, includes means for limiting a position of the damping wire on the no-hole region of the shadow mask
It is to be understood that both the foregoing general description and the following detailed description are exemplary and explanatory and are intended to provide further explanation of the invention as claimed.